So let me preface this by saying that it's very possible that I will make some face-palmimg statements here, and for that I apologize, bit we all have to learn at some point I have a 71 Riviera with the 455 and last year she started knocking so I figured the time was right to do some slight modifying. It's not a racecar and I didn't want to make it one, but I wanted a little extra power. So the engine is rebuilt and is completely stock with the exception of .030 overbore, TA 212 cam w dual grooved bearings, and the TA timing cover with blueprinted oil pump. I am trying to determine where my timing should be set at, and I have read the power timing thread, but I feel like I'm missing some crucial information that makes it not sound like a foreign language. This is my first foray into older engine tech and I want to make sure I'm not breaking things. Any advise is greatly appreciated!
First, let me say that if you think that you are seeing a foreign language when you read the Power Timing thread, then the crucial information you are missing is an understanding of ignition system basics, what a distributor does, and how the mechanical and vacuum advance systems actually function inside that distributor. You can get all of that by reading (and rereading if necessary) the ignition chapter of a Buick Chassis manual, or with a couple of Google searches for that matter. Once you understand the actual function of parts, it will make more sense to you. BTW, if you send an e mail to the address in my signature, I will send you a pdf of the ignition chapter of the 1971 Buick Chassis Manual. Where your initial timing needs to be set will depend on the distributor that is currently installed in the engine. Unless you have owned the car from new, you can't say it is the same distributor it left the factory with. The car is 46 years old. The distributor that should be installed in a 1971 455 is 1112077. If there is a different distributor installed in the engine, it could be very different inside when it comes to the amount of mechanical advance. The part number is on the circumference of the distributor just under where the cap contacts the base. Start there. What distributor part number is installed in your engine?
1972 455 distributor. Very similar to the correct 71 distributor, and maybe if your car was late production, that is what they installed. It has between 14 and 18* of mechanical advance.
Ok. I don't think that the vacuum advance is working on it though. After setting initial and plugging it back in, the timing isn't advancing at idle. It's currently plugged into manifold vacuum because that's how the routing diagram has it, but I know there are different opinions on manifold vs ported for vac advance. And I guess my next question would be; should I change out the distributor? The engineering heavily modified but I want to get the best performance out of it that I can.
Just change out the vacuum advance. That's a good distributor, I'd keep it. Your initial should be up around 14* with that distributor.
Here are the specs for that distributor, notice the maximum mechanical advance is 14-18* @ 2900 RPM. Due to the manufacturing tolerances of the day, YOUR distributor could be anywhere in that range. You want your maximum total timing at WOT to be 30-34*. This does not include vacuum advance since there will be no vacuum at WOT. If your maximum mechanical advance is closer to 18*, then an initial timing of 14* will produce a total timing of 14 + 18 = 32*. If it is closer to 14* then you will need more initial to get to 32*. You can verify all that with a timing light.
How the distributor was calibrated when new, versus what it does now that it has decades of wear can be two different things. I've seen plenty of old points distributors that had entirely missing limit bushings. HEI distributors with worn pivot pins and weight holes are epidemic. The distributor has to be in usable condition before any of the calibration can be trusted.
